negative regex for perl string substitution

Question

I'm trying to shorten all multiple spaces to one space, except for the first occurence of spaces (indentation).

I've found that this code will replace the first occurences:

$_ =~ s/^ +/ /;

So I thought, its negation will do what I want. But it does not:

$_ =~ s/!^ +/ /g;

What am I doing wrong?

score 2 · Accepted Answer · answered Nov 10 '15 at 17:25

2

You can change approach to the regex

s/\S\K +/ /g;

answered Nov 10 '15 at 17:25

mpapec

1

Non space, keep it, followed by one or more spaces, replace with space. (and the bit you kept). I think? But a nice solution. – Sobrique Nov 10 '15 at 17:30
nice idea, yes or `(?<=\S) +` – bobble bubble Nov 10 '15 at 17:34
Yes, \K is positive look behind from v5.10 and newer. – mpapec Nov 10 '15 at 17:40

score 1 · Answer 2 · answered Nov 10 '15 at 17:24

1

Exclamation mark is not negation in regex. At least, not like that.

What you need is negative lookbehind:

s/(?<!^)\s+/ /g;

Should do the trick.

answered Nov 10 '15 at 17:24

Sobrique

Yes. It matches any whitespace. Easy enough to be more selective though. – Sobrique Nov 11 '15 at 22:56

2 Answers2